Crude oil products are globally obtained from subterranean reservoirs using techniques such as drilling and hydraulic fracturing. Transportation of crude oil products from the subterranean reservoir, required to process, i.e. refine, the crude oil, is accomplished by moving the crude oil through pipes and into storage/transportation means such as rail cars, tanks, and the like. During the moving, production, and/or storage, the crude is often subjected to ambient temperatures between −40° C. and 60° C.
Crude oil products include linear and branched alkanes having the general formula CnH2n+2 wherein n is typically about 1-50, although minor amounts of longer hydrocarbon chains do occur. The higher molecular weight alkanes can be problematic in that their melting points tend to be greater than ambient temperatures in some cases. For example, nonadecane has a melting point of 33° C.; higher alkanes can have melting points in excess of 60° C. for example.
The high melting alkane fractions lead to formation of paraffinic residue that solidifies and deposits on the sides and bottoms of pipes, storage vessels, and transportation vessels (rail cars, ocean tankers, etc.). The solidified paraffinic residue, also known as “paraffin wax”, not only reduces the effective volume of the structure it is contained within but also represents a loss of a valuable component from the body of the crude oil. Paraffin wax build up, especially excessive paraffin wax buildup reduces the efficiency of transporting crude oil and leads to increased costs related to added downtime for cleaning of the pipes and/or vessels as well as disposal of residues removed from the vessel which increase environmental burden. While the pipelines and vessels can be cleaned to remove the paraffinic residue, the process generates hazardous waste, takes the vessel out of service during the cleaning period, and is expensive.
The formation of paraffin wax can be reduced by “paraffin inhibitors” (PI) which interfere with the crystallization process of wax and/or suspend wax crystals in the oil. The addition of PI to the crude oil is effective in dispersing the paraffinic residue, thereby reducing the formation of residues in the pipelines and vessels to the benefit of the oil and gas industry. The PI effectively reduce the formation of paraffinic residues during storage and transportation of the crude oil products, mitigating economic loss and decreasing environmental impact.
Typical paraffin inhibitor polymers include, e.g. ethylene polymers and copolymers thereof with vinyl acetate, acrylonitrile, or α-olefins such as octene, butene, propylene, and the like; comb polymers with alkyl side chains such as methacrylate ester copolymers, maleic-olefinic ester copolymers, and maleic-olefinic amide copolymers; and branched copolymers having alkyl side chains such as alkylphenol-formaldehyde copolymers and polyethyleneimines.
Nonaqueous formulations including such paraffin inhibitors as concentrate (“PIC”) must also be transported to, and stored at the field locations where crude oil is recovered so that it can be applied as needed to the contents of the pipes, vessels, and the like. Providing PIC in a fluid format—i.e. in solution or dispersion—is highly advantageous for applying PI in the field because pumping equipment suitable to meter the desired amount of PI into a pipe or vessel is readily available. However, severe dispensing and usage problems are associated with the use of nonaqueous paraffin inhibitor concentrates (PIC) in areas where the winter temperature goes well below 0° C. In some field locations, for example, a winter temperature of −10° C. or less, −20° C. or less, −30° C. or less, or even −40° C. or less is not unusual. In such temperatures, PICs tend to form a gel or a solid (with the PI polymer solidifying or precipitating from the PIC liquid) with decreasing temperature, leading to the aforementioned severe dispensing and usage problems.
Previous solutions to the problem of PIC solidification include the addition of relatively large amounts (e.g., more than about 20 wt % or vol %) of low-boiling point solvents, such as methanol, to the PIC compositions. However, use of such large amounts of solvents can pose many different problems. The previous solutions formed dispersions of PI polymers in solvents. Often times the dispersed formulations were milky. The dispersions included larger particles sizes which limited the applicability in situations such as capstringing. Over time, the PI polymers tend to settle out of the dispersions. Even at higher concentrations (e.g., more than 20 wt % or vol %) of low-boiling point solvents, the paraffin inhibiting compositions still tend to freeze solid within days. At higher temperatures, systems containing large amounts of low-boiling point solvents can have a substantial vapor pressure, even dangerous overpressures which can lead to rupture of storage tanks. While cold temperatures are of concern to crude oil field operations, temperatures of up to about 60° C. are also encountered—often at the same field locations, depending on the seasonal weather patterns. It would be advantageous to provide additives for PICs that reduce the formation of solids therein from −40° C. to 60° C., thereby allowing the pumping of the PIC in the field within this temperature range and without buildup of high vapor pressure at the upper end of the range.